Aurora kinase is a serine/threonine kinase involved in cell division. With regard to the Aurora kinase, three subtypes of A, B and C are known at present, and they have very high homology to each other. Aurora A participates in the maturation and distribution of centrosome or in the formation of spindle body. On the other hand, it is believed that Aurora B participates in the aggregation and pairing of chromosome, a spindle checkpoint and cytoplasm division [Nat. Rev. Mol. Cell. Biol., No. 4, pp. 842-854]. Also, it is believed that Aurora C acts similarly as a result of interaction with Aurora B [J. Biol. Chem., Epub ahead (2004)]. From the fact that high expression of Aurora A has been hitherto confirmed in many cancer cells; that high expression of Aurora A in normal cells leads to transformation of normal cell strains of rodent; and the like, Aurora A, being one of oncogenes, is recognized to be an adequate target for an antitumor agent [EMBO J., No. 17, pp. 3052-3065 (1998)].
There is another report that cancer cells in which Aurora A is highly expressed have a resistance to paclitaxel [Cancer Cell, Vol. 3, pp. 51-62 (2003)]. Meanwhile, with regard to the Aurora kinase inhibitor, development of subtype-selective drugs has been thought to be difficult in view of high homology among subtypes, protein structure analysis and the like; and although there have been known reports on drugs such as ZM447439 which inhibit both Aurora A and Aurora B at the same time [J. Cell Biol., No. 161, pp. 267-280 (2003); J. Cell Biol., No. 161, pp. 281-294, (2003); Nat. Med., No. 10, pp. 262-267, (2004)], no report concerning Aurora A selective drugs have been known. Thus, in those reports, disclosed is the antitumor effect only for the case where a drug which inhibits both Aurora A and Aurora B at the same time is solely administered. In addition, there has been also reported a result that in a drug which inhibits both Aurora A and Aurora B at the same time, the Aurora kinase inhibiting action attenuates the action of paclitaxel [J. Cell Biol., No. 161, pp. 281-294, (2003)].
Now, patent applications concerning compounds having an Aurora kinase inhibiting action have been previously filed (WO 02/057259, U.S. Pat. No. 6,664,247, etc.), and patent applications concerning aminopyridine derivatives has been filed as well (U.S. Pat. No. 6,586,424, etc.). Under these circumstances, the present inventors filed a patent application directed to an aminopyridine derivative having an excellent Aurora A selective inhibitory action (WO2006/046734).